(1) Field of the Invention
The present invention relates to the field of displaying graphics subtitles.
(2) Description of the Related Art
The term “graphics subtitles” relates to a technique of displaying subtitles by decoding graphics data compressed using run-length coding, and this technique has been used in the field of BD-ROM playback apparatuses as well as the field of DVB-MHP and DVD-Video. Generally, graphics subtitles are displayed by decoding a graphics subtitle stream. A graphics subtitle stream is a sequence of PES packets and such PES packets include packets containing graphics data, packets containing pallet data, and packets containing control data. The graphics data is run-length data that represents runs of the identical code values by counts of the same code values occurring consecutively.
The pallet data associates each code value with brightness and color difference. The control data includes a reference value specifying a specific piece of pallet data to be used for color conversion, information defining a display area on the plane memory for rendering graphics, and information defining the display coordinates of the graphics on the plane memory. The pallet data instructs the graphics display and color conversion based on the reference value.
The processes required to be performed by a playback apparatus for rendering graphics subtitles are limited to: decompression of run-length data, rendering to the plane memory, color conversion with reference to the color lookup table, and so on. Thus, the entire processing by the playback apparatus to display subtitles is simplified.